There is a storage system in which a server and a storage apparatus are coupled via a network. In the storage system, identical data is stored in each of multiple data storage areas of the storage apparatus so as to prevent loss of data or distribute the load. To write identical data into each of multiple data storage areas is called “mirroring.”
The mirroring relation between the multiple data storage areas is sometimes broken. If the mirroring relation is broken and then a mirroring relation is reestablished, data stored in one data storage area is copied to the other data storage area. Related-art examples include Japanese Laid-open Patent Publication No. 2002-373093 and Japanese Laid-open Patent Publication No. 2007-249652.
Pieces of data stored in the data storage areas are different from one another until a copy process is completed. Therefore, the server cannot access data stored in a copy-destination data storage area until the copy process is completed.